The present invention relates to joint mechanisms, and more particularly, to a spherical joint mechanism useable to provide spherical or circular motion about a particular point.
Various types of joints have been used to provide spherical motion. For example, a conventional ball joint where a convex hemispherical ball slides within a concave hemispherical socket may be used to provide spherical motion. In a ball joint spherical motion occurs about the center of the ball within the socket at the center of rotation. Spherical rotation does not occur about a point located outside of the ball joint thereby limiting spherical movement.
Other types of joints may also provide spherical motion. For example, Hooke, Cardan, and Universal joints are mechanisms whose links lie on the surface of a sphere, and the access of the pivots between links pass through the center of rotation. In these types of joints, the center of rotation may not be occupied by any part of the mechanism. However, access to the center of rotation may be obscured by the moving links and the center of rotation surrounded by the mechanism. With these types of joints, it is possible to have one or more joints share a common center of rotation. However, the interface between mechanisms often greatly reduces the range of motion of each joint.
Sliding spherical joints are also used to provide spherical motion about a point. In this type of joint, a mechanism slides on the inside of a hemispherically shaped track. Also, two crossed semicircular tracks may be used to carry a moving point wherein one track slides within the other track. This type of mechanism may not have unrestricted access to the center of rotation because the tracks extend around the center of rotation to provide a desired range of motion. Using this type of joint, multiple joints may also share a common center of rotation. However, the addition of each joint further reduces the available range of motion.
In addition to basic spherical joints, a number of joints have been developed for attaching a number of struts together. Beavers, U.S. Pat. No. 4,450,851, describes a "hub assembly" for a collapsible tent. DeLorme, U.S. Pat. No. 4,521,998, shows a "universal hub" for geodesic type structures. In both cases, the hub assemblies are primarily designed to connect struts together on the surface of a framework. The hubs only allow the struts to radiate outward roughly in a single plane (or on the surface of a cone).
Ventrella (U.S. Pat. No. 4,480,418) describes a joint for use in building "space grid structures" which allows struts to radiate out in all directions, but the spherical motion of the members is very limited.
In none of these assemblies are the centers of rotation of the attached struts concentric. This may cause two problems. First, compressive and tensile forces in the struts causes twisting moments on the joints, and the forces are not transmitted to the other struts as in an ideal truss. Second, in a controlled structure, such as a variable geometry truss robot, the motions of the mechanism in response to changing strut lengths is much more difficult to model.
It is therefore desirable to achieve a joint mechanism which provides a greater range of motion than in ball joints or Universal joints.
Moreover, it is also desirable to achieve a joint mechanism where the linkages obscure only a small section of an imaginary sphere located about the center of rotation of the joint mechanism in order to allow, among other things, that several joint mechanisms be used to share a common center of rotation.
It is also desirable to connect a plurality of joint mechanisms to comprise a concentric spherical joint mechanism having a common center of rotation wherein truss assemblies may be constructed using a plurality of concentric spherical joint mechanisms.
It is also desirable to provide a joint mechanism which provides for spherical or circular rotation about a center of rotation where it is undesirable or impossible to have portions of the mechanism located at the center of rotation.
It is also desirable to achieve a concentric spherical joint mechanism having multiple joint mechanisms thereon whereby the members are capable of radiating outward in all directions.